Vodacom is unable to manage their billing propper

I am really so sick and tired of issues with Vodacom. First they messed up my phone upgrade and put me on a flexi 500 contract instead of a flexi 50. Now they want to tell me that I am in arrears with my account after they had to credit me for deducting the wrong ammounts from my account. I spoke to Ewert the manager in the store in centurion and he really tried his best to help me with this . However even after Vodacom received my bank statements showing them where my payments has been made they still want to tell me my account is in arrears. I spoke to a lady now that still does not understand the amount that she wants me to pay is supposed to have been credited to my account. THIS IS REALLY UNACCEPTABLE. You can not phone and speak to someone to help you each department directs you to another department. I even received a letter stating that if I do not make payment in 7 days I will be required to pay up the contract and I will be black listed. Now Vodacom please understand me loud and clear. I WILL NOT PAY YOU MONEY FOR SERVICES I DO NOT HAVE. If this problem is not resolved before the end of this week I will lay a complaint at the consumer laws. I had enough now.